This invention relates to a method and apparatus for replenishing the processing liquid in an automatic film processor to compensate for the lowered chemical activity of the processor liquid which results from the processing of film.
It has been recognized in the prior art that a preferred way to control the rate and amount of replenishment supplied to the processor is to sense the image density of the film passing through the film processor and to drive an electrical control signal proportional to said image density which controls the replenishment means for said film processor.
The prior art replenishing systems fail to energize the replenishing pumps unless the density measuring signal indicates a need for replenishing liquid. Thus if the machine is inoperative for long periods of time (with no film passing through) and the processing liquid in the tank becomes ineffective due to oxidation, there would be no replenishment of the liquid with such equipment. These prior art systems require a certain minimum quantity of film to pass through processors before actuation of the replenishing pumps so that if a substantial quantity of film has passed through (but less than the minimum quantity required to energize the replenishing pump) and then the processor is not used for a period of time, the condition of the processor liquid deteriorates at an exponential-like rate so that it requires more replenishing liquid than can be supplied by the next cycle. This causes improper processing until sufficient replenishing liquid is supplied to bring the condition of the liquid back up to standard. This would necessitate manual assistance to prevent an unacceptable batch of film from being processed.
With the instant invention however, the replenishing pump is automatically energized at predetermined time intervals (e.g. every 30 seconds) regardless of the film density, and if the density measuring system fails to call for replenishing liquid as in the case of non-use or zero density the pump will be automatically shut off almost immediately (e.g. 20 milliseconds). By inserting a counter to count the number of non-use or zero density pump starts, an automatic replenishment cycle can be readily provided to run a second pump for a preset time after a predetermined number of such non-use or zero density start-stop cycles or after a predetermined number of cycles regardless of the density or use of the film and processor, respectively.
This invention relates to an improvement for this type of replenishment technique. It is an object of this invention to provide a method and means for replenishing the processing liquids of a film processor which is based on both the sensed image density of the film and the velocity of the film through said film processor.
It is a more particular object of this invention to provide replenishment means to maintain the chemical activity of the developing and fixing chemicals in the film processor when there is no film passing through the film processor or when said film processor is not being used.